(1) Field of the Invention
This invention relates to purifying liquids. More particularly, the invention relates to a method of and an apparatus for purifying drinking water for domestic, office, plant, restaurant, hotel and similar use.
(2) Description of the Prior Art
It is common practice to purify drinking water by addition of chemicals to the water. The most common chemical treatment is by the addition of chlorine to water. However, the use of chlorine has long been questioned. For several decades Western European scientists, such as Torricelli, have believed that continual absorption by the human organism of small quantities of chloring produce diseases such as hardening of the arteries and damage to liver and kidneys. Torricelli, Alfred. Drinking Water Purification. Adv. Chem. Ser. 21:453-465. (1959)
In 1928 Duggeli published a paper questioning the ability of chlorine to function effectively as a bactericide. He concluded that chlorine was a rather slow working bactericide and that either a low temperature of the water or a high percentage of organic matter in the water greatly slowed down the bactericidal action of chlorine. He also reported that small doses of chlorine did not kill bacteria but only paralyzed them thus making possible subsequent return to normal bacterial growth rates. He also found that, in order to obtain an absolutely lethal bactericidal effect with chlorine, a rather high dosage of chlorination must be used. It has also been found that the ability of chlorine to work as a bactericide is highly sensitive to parameters in the water, that is, the length of time the chlorine is in the water, the presence of heavy metals, the pH and the temperature of the water. Thus, for effective sterilization of water, precise and certain conditions must be established in order to obtain the desired results. Travaux de chimie alimentaire et d'hygiene 1926-1928 "Beitrag zur Frage der Wirkung von Chlor auf die Bakterien des Wassers."
More recently, studies have shown that several of the chlorinated hydrocarbons are carcenogenic. EPA Environmental News, EPA Releases Results of National Drinking Water Survey. April 1975. R-89. The United States Environmental Protection Agency's National Survey conducted on potable water in 1975 indicated that chlorinated hydrocarbons, several of them carcenogenic, existed above permissible levels in seventy-nine cities. In only two cities tested were the levels of chlorinated hydrocarbons below the permissible level. Both of these cities used ozone to treat water. Internal Ozone Institute. Press Release: Ozonation produces highest quality U.S. Drinking Water. Apr. 28, 1975.
The ability of ozone to purify drinking water has been appreciated for some time. According to Bringmann, the rate of destruction of bacteria by ozone is 1 to 2 orders of magnitude faster than that of chlorine. (1) Bringmann, G. 1954. Determination of the lethal activity of chlorine and ozone on E. Coli, Z. Hyg. Infektionskr. 139: 130-139. (2) Bringmann, G. 1954, Die Wirkung von Ozon auf Organismen des Trinkwassers, (The action of ozone on organisms in water) A. Hyg. Infektionskr. 139: 333-337. Fetner and Ingols have reported that the bacterial action of chlorine is progressive while the bacterial action of ozone is sudden after reaching threshold value. Fetner, R. H., and R. S. Ingols. 1956. A Comparison of the Bactericidal Activity of Ozone and Chlorine Against Escherichia Coli at 1.degree.; J. Gen. Microbiol, 15(2): 380-385. Kessel et al have shown that polio virus treated with chlorine to a residual value of 0.5 mg per liter to 1 mg per liter will be rendered inert in 11/2-3 hours while treatment with ozone to a residual value of 0.045 to 0.45 mg per liter will render polio viruses inert in only two minutes. Kessel, J. F., D. K. Allison, F. J. Moore, and M. Kaime. Comparison of Chlorine and Ozone as Virucidal Agents of Poliomyelitis Virus. Proc. Soc. Exp. Biol. Med. 53(1): 71-73. 1943.
There are many publications that disclose the benefits of treating water with ozone. To summarize, these publications disclose that ozone treatment systems in general are capable of removing the following undesirable substances from water: organics, heavy metals such as manganese, pathogens such as virus, spors, fungii, mercaptans and E. coli bacteria, formaldehyde, pesticides, detergent and chlorine and halogenated hydrocarbons.
The conventional method of dissolving ozone in water is to bubble the gaseous ozone upwardly through the water. U.S. Pat. No. 3,699,776 discloses an ozone purifier for a pressurized water cooler wherein gaseous ozone is introduced through a diffuser into a tank containing water. The ozone is allowed to bubble through the water.
U.S. Pat. No. 3,726,404 discloses an apparatus for purifying water wherein a batch of water is contained in a tank and fine bubbles of ozone are allowed to rise through the water. Once the batch of water is treated with a sufficient amount of ozone, the batch is transferred to a storage tank.
U.S. Pat. No. 3,421,999 discloses an ozone generator for purifying contaminated fluid wherein ozone is injected through an aspirator into a stream of contaminated fluid. The mixture of ozone and fluid is then immediately discharged into a pipeline which directs the fluid to storage.
U.S. Pat. No. 3,692,180 discloses a water purifier wherein ozone is fed to the bottom of a container. A diffuser breaks the ozone into small bubbles that rise through the water in the container.
U.S. Pat. No. 2,970,821 discloses a water treatment system wherein ozone is introduced directly into a water line through an injector. Immediately after the injection of ozone the water is added to a mixing vessel wherein the ozone and water are mixed and the water treated.
The above-mentioned patents disclose systems wherein ozone is bubbled through water. Although a portion of the ozone is dissolved in the water, the dissolution rate of ozone into the water is very low because of the generally low partial pressure of ozone in the water. Thus, the treatment time is extended, and, when the ozone bubbles reach the surface of the water, the bubbles burst and a large amount of undissolved ozone is wasted.
One object of the invention is to provide a water treatment system wherein purified water may be continuously produced.
Another object of the invention is to provide a system which provides for large amounts of ozone to be dissolved into water.
Another object of the invention is to contact the water with ozone bubbles for relatively long periods of time to provide for dissolution of the ozone into the water.